The present application relates to contact structures for semiconductor devices, and more particularly, to a source contact structure and a drain contact structure (collectively referred to hereinafter as source/drain contact structures) having low contact resistance and improved electromigration properties.
Field Effect Transistors (FETs) are essential components of all modern electronic products. Generally, after a transistor is formed, contact structures are made to connect a source region, a drain region, and/or a gate region of the transistor to make the transistor fully functional. Traditionally, the contact structures are typically formed of tungsten (W). However, as circuit densities are increased, the aspect ratio of contact structures has increased and adequate plating of such high aspect ratio contact structures with W has proven difficult. W-based contact structures suffer from gap fill issues. Oftentimes, seams or keyholes are formed within the contact structures. The presence of seams or keyholes negatively affects contact performance.
Copper (Cu) and Cu alloys are materials that are increasingly used in the fabrication of contact structures due to their low electrical resistance and excellent reflow properties at low temperatures which prevent seam/keyhole formation. Despite these advantages, Cu-based contact structures are more susceptible to electromigration. Cu readily diffuses into the active device regions (e.g., source/drain regions), thus causing leakage of FETs. Therefore, there remains a need to develop contact structures with low electrical resistance and improved electromigration properties.